The present invention generally relates to image processing technologies. More particularly, the invention relates to image correcting apparatuses and methods that correct images on which persons are photographed.
In preparing photo prints from digital image data, which is, for example, acquired by photo shooting with a digital camera, or obtained by photo-reading of an image printed on a photo film, correction may be performed on the images so that the images are reproduced with appropriate colors and densities. In particular, when it comes to images on which persons are photographed, it is significantly important to reproduce face colors appropriately.
There have been known image processing methods that place an importance on skin colors of persons, including, for example, a technology (refer to JP 2000-196890 A) in which a person face is automatically extracted from image data and the data is corrected so that a skin color of the face area achieves a target range of density, and a technology (refer to JP 2000-182043 A) in which a person face is automatically extracted from image data and the data is corrected so that a skin color of the face area achieves a target chromaticity.
In these technologies, a target density and/or a target chromaticity of skin colors are pre-set and the images are corrected respectively in such a manner that the density and/or color of the face regions extracted from the image data are close to the target values. Accordingly substantially appropriate correction can be performed as long as the persons on the images to be corrected are from the same race as is used in presetting the target values of density and chromaticity of skin colors.
However, considering that different persons from different races have different skin colors, there may be problems if a certain color and/or density is used as a skin color target for correcting all the images of an image group, when the images include different persons from a plurality of races and are shot under identical shooting conditions (such as class book photos). For example, there may be inconsistency in background colors among the images or skin color tint may not always be appropriately reproduced. Therefore, it is desirable to perform identical correction to an image group consisting of such a plurality of images.
In JP 6-208178 A, on the other hand, a photo printing method for printing a plurality of image frames that have been shot on a photo film by a camera with an auto-exposure function, using so-called direct exposure photo printing in which an image shot on a photo film is projected and exposed onto a photosensitive material (photographic paper) is described. In this method each of the plurality of image frames is divided into multiple pieces and subjected to photometry. According to the result of the photometry, an identical exposure amount is determined. Images equivalent to print images that would be obtained by printing the image frames using the predetermined identical exposure amount are displayed on an image display unit. One or more displayed image frames are checked and modified to determine a modification exposure amount for the image frames. Based on the identical exposure amount and the modification exposure amount, a printing exposure amount for the image frames is determined. Using the printing exposure amount thus obtained, the plurality of image frames are printed onto a sheet of photographic paper.
According to the method, one or more frames (including all frames) out of the images contained in the same film can be displayed on the image display unit to determine a modification exposure amount for each of the images. The modification exposure amounts are averaged to determine the printing exposure amount, which is then used for printing all the images in the film. Therefore, possible variations in the background colors among the images shot under identical shooting conditions can be prevented.
However, if modification exposure amounts are determined for all of the images contained in a film, one by one, a significant time is required for the process of checking and determining modification values for the displayed images. On the other hand, if the modification exposure amount is determined using only one frame, such amount may not reproduce skin colors with appropriate color and/or density for other frames, in particular, in case where persons from different races having different face colors mixedly exist in the frames.